Project Summary

Project Abstract:
Electrically conductive asphalt composite is a promising multifunctional construction material with the potential for self-sensing, self-healing, and various non-structural applications that can lead to technical innovations for sustainable pavement. While such multifunctional applications of conductive asphalt requires precise control of conductivity, a rapid transition from insulated to conductive phase as the conductive additive increases, known as percolation threshold, hinders the conductive asphalt from practical applications. This study aims to remove the percolation threshold from the electrical resistivity curve of asphalt composite for making the multifunctional applications practically feasible. Various conductive fillers with different crystal structures will be tested for this purpose. In addition, selection of conductive fibers will reduce the amount of conductive filler and make the cost for conductive asphalt cheaper. A method of controlling asphalt conductivity will be developed through the tests for asphalt mastic, asphalt mortar, and asphalt concrete with various additive combinations.

Project Objectives:
The objective of this study is to find a proper combination of conductive additives that enables smooth transition from insulated to conductive phase. Following subjects will be investigated through this study;

1) The effect of graphite types and amounts on the conductivity of asphalt mastic (asphalt binder + fillers)

Task Descriptions:Task 1. Conductivity control of asphalt mastic (asphalt binder + fillers)
Various conductive fillers (graphite powders with different particle sizes and crystal structures) will be mixed with asphalt binder and their electrical resistivity will be measured to sort out the effective conductive fillers. The relationship between electrical resistivity of mastics and the amount of conductive fillers for each graphite type will be obtained to find the conductive filler enabling smooth transition of the conductivity.

Task 2. Crystal structure of conductive fillers
The crystal size and shape of the various graphite powders will be investigated using scanning electron microscope (SEM) to provide a physical explanation for their different effects on conductivity.

Task 3. Conductivity control of asphalt mortar (asphalt mastic + fine aggregate)
The conductive fillers selected from the Task 1 will be tested with different sand-bitumen ratio to investigate the effect of fine aggregate on the mortar conductivity.

Task 4. Conductivity control of asphalt concrete (asphalt mortar + coarse aggregate)
Conductivity of asphalt concrete will be investigated. The effect of conductive fillers on percent air-void and indirect tensile strength will be investigated. In addition, the effect of steel fibers on the conductivity and the problems in mixing and compaction caused from the conductive additives will be investigated. Prototype specimens of the conductive asphalt concrete, tailored for the most probable multifunctional applications will be produced.

Task 5. Documentation
A final report documenting the findings of the study will be prepared and submitted to SWUTC.

Implementation of Research Outcomes:The key findings of this research is a method of controlling electrical conductivity of asphalt concrete, which is the most common paving material that is inherently non-conductive. The traditional function of the asphalt concrete is the mechanical performance to resist traffic loads and environmental degradation. The conductivity control enables asphalt pavements to have various non-structural and non-traditional functions such as self-healing, self-sensing, deicing, and tele-communication. In addition, the conductive pavement can be utilized for some developing technologies such as a guide for autonomous (driverless) vehicles and connected vehicles. The PI of the project has submitted and is preparing several research proposals on multifunctional pavements using conductive asphalt concrete. The conductive pavement is a new, but actively investigated concept in transportation engineering, and the results of the research will provide a technical basis to the development of multifunctional pavement technology.

Planned Presentation: Controlling Electrical Conductivity and Mechanical Performance of Asphalt Concrete with Conductive Additives, Y. Rew and P. Park, to be submitted for presentation to the 2015 Transportation Research Board Annual Meeting, January 2016.

Journal Article in Preparation:Controlling Electrical Conductivity of Asphalt Binder Using Graphite, P. Park, A. Baranikumar, A. V. Tamashausky and S. El-Tawil, to be submitted to Construction and Building Materials.

Journal Article in Preparation: Controlling Electrical Conductivity and Mechanical Performance of Asphalt Concrete with Conductive Additives, Y. Rew, A. Baranikumar and P. Park, to be submitted to Transportation Research Board.

Impacts/Benefits of Implementation:The results of this research will provide the basis for new multifunctional electrical applications of pavements. Which in turn can improve transportation safety and service life, and reduce user and agency costs for construction and maintenance of transportation systems.